Drill string members are used to transmit rotational force to a drill bit during the drilling of an oil or gas well in the form of a multiplicity of pipe sections consecutively threadedly engaged. Prior to attachment to the drill string, the drill string pipe sections or members are handled individually such that the threads at each end are subjected to potential damage or destruction. To prevent this damage and prolong the useful life of the drill string member, devices have been constructed in the past to be placed over the threads of the pipe of the drilling string section during storage and handling. The devices are removed just prior to attachment of the pipe section to the drill string and reused on subsequent drill string members.
For instance, U.S. Pat. No. 2,141,381, issued to Engstrom, shows such a protective device constructed of a rigid outer ring having an inner surface adapted to engage the external threads of the pipe section and having a mechanical latch apparatus for constricting the outer rigid shell so as to affix the pipe thread protector to the drill string member.
U.S. Pat. No. 2,547,992, issued to Baker, shows a pipe thread protector having a rigid cylindrical outer shell which fits over the external threads of the pipe of the drill string member utilizing a complex cam actuated mechanical linkage apparatus to affix the thread protector to the pipe section. U.S. Pat. No. 2,880,761, issued to Peter, shows a bifurcated cylindrical rigid shell longitudinally hinged which includes alternating eyelets formed on opposing edges which may be engaged by a pin so as to constrict the thread protector on the drill string member.
U.S. Pat. No. 4,033,380, issued to Weber, shows a one piece thread protector constructed of a plastic material formed into a cup like structure which is forcibly mounted over the exposed threads of the drill string member and is thereby frictionally affixed.
However, these and other devices for the protection of threads on pipe sections suffer from several inefficiencies. For instance, designs using complex mechanical structures to affix the pipe thread protector are subject to great stress and must freguently be repaired or replaced. Deformation may loosen the grip of the thread protector upon the drill string member to the point of dislodgement.
Devices which rely on mere frictional contact with the thread surface offer a simplier design but are generally easier to dislodge during handling, or the coefficient of friction between the thread protector and the drill pipe threads may be reduced by the presence of contaminants such as drilling fluid, water, mud, or other fluids frequently encountered at drilling sites to the point where slippage occurs.
Therefore, it becomes advantageous to construct a pipe thread protector which obviates the inefficiencies of conventional designs by adhering to the threaded portion of a drill string member without relying on complex, easily damaged mechanical latching mechanisms, yet assuring an adequate force adhering the pipe thread protector to the drill string member.